Co-extrusion print heads allow two or more materials to be extruded simultaneously onto a substrate. These materials often consist of slurries, liquids loaded with particles. Examples of co-extrusion print heads and their applications can be found in U.S. Pat. Nos. 7,799,371; 8,117,983; and 7,780,812; as well as US Patent Publication Nos. 20100505 and 20121539. Some applications use highly-loaded slurries, such as for battery electrode manufacture. The extrusion process of these slurries, especially the highly-loaded slurries, sometimes causes the formation of an edge bead, shown in FIGS. 1 and 2.
FIG. 1 shows a monolithic thin film formed of one material 10 having an edge bead 12. FIG. 2 shows a thin film formed of at least two materials 14 and 16, having an edge bead 18. However, for most films a variation of less than 2% in thickness is desired. Typically, some sort of mechanical or chemical post processing is performed that removes the edge beads. This can add to the overall processing time or hardware complexity.
Some of the approaches used to eliminate edge beads include feeding extra polymer into the extrusion process to provide a controllable edge, which can then be cut away after drawing the film from the die, as in U.S. Pat. No. 4,348,346. Another approach uses compressed gas to push down on the sides to force the edge beads down, as shown in U.S. Pat. No. 5,398,372. Another approach uses a deckle, or fence, to control the edge bead, as in U.S. Pat. Nos. 3,797,987 and 3,694,132. A similar approach is shown in US Publication No. 20130020737 with an edge sculpting mechanism.